反义RNA表观遗传沉默导致癌相关基因激活的致癌新机制研究

The epigenetic mechanism of silencing of tumor suppressor genes in cancer cells has been well known. However, the epigenetic mechanism underlying the activation of oncogenes or cancer-associated genes is unclear yet. In addition, the anticancer mechanism of DNA methylation inhibitor (5-Aza-2 '-deoxycytidine, AZA) is still puzzling. Previously, we found that antisense RNA p15AS can inhibit the expression of tumor suppressor gene p15 through epigenetic mechanisms. Preliminary studies have shown that many cancer-associated genes in human genome have antisense RNAs. Therefore, we hypothesized that the activation of cancer-associated genes may be attributed to the epigenetic silencing of antisense RNAs in tumor cells and AZA may play its role in treatment of cancers through activation of antisense RNAs which can down-regulate the expression of cancer-associated genes beside of activation of tumor suppressor genes and the innate immune pathway genes. This study includes: (1) genome-wide screening and identification of antisense RNAs derived from cancer-associated genes; (2) determination of the relationship between cancer-associated genes and their antisense RNAs in expression and regulation;(3) determination of epigenetic mechanism by which antisense RNA genes was silenced; (4) determination of the molecular mechanism by which cancer-associated genes are regulated by antisense RNAs. This project is unique and innovative, and the results will clarify a new epigenetic mechanism of carcinogenesis and are of great significance to both basic and clinical researches.

肿瘤抑癌基因沉默的表观遗传机制已广为人知，但癌相关基因激活的表观遗传机制至今尚不清楚。此外，表观遗传学药物5-氮-2’-脱氧胞苷的抑癌机制至今仍使人疑惑。我们已发现反义RNAp15AS可以通过表观遗传机制抑制抑癌基因p15的表达。初步研究表明，人基因组中许多癌相关基因存在反义RNA。因此，我们提出假说：肿瘤癌相关基因的激活可能归因于其反义RNA的表观遗传沉默；DNA甲基化抑制剂的抑癌作用除了激活抑癌基因和激活天然免疫通路基因外，也可能通过激活反义RNA从而下调癌相关基因的表达。本研究内容包括：（1）癌相关基因的全基因组反义RNA的筛选和鉴定；（2）反义RNA与对应癌相关基因的表达和调控关系研究；（3）癌相关基因反义RNA表达的表观遗传调控机制研究；（4）反义RNA调控癌相关基因的分子机制研究。本项目具有独特创新性，将阐明一个新的致癌表观遗传学机制，对基础研究和临床医学研究均具有重要意义。

几乎所有类型肿瘤细胞的原癌基因都被异常激活。然而，其激活的表观遗传学机制尚未完全阐明。本研究项目中，我们发现部分原癌基因，包括c-MYC，拥有反义RNA。癌组织中c-MYC的上调归因于其反义RNA MYC-AS1通过DNA甲基化而沉默。反义RNA MYC-AS1通过RNAi机制抑制c-MYC的表达，在体外显著抑制癌细胞增殖，并在体内阻碍裸鼠肿瘤生长。 反义RNA MYC-AS1直接与细胞质中的HuR蛋白结合，增强了MYC-AS1的反义RNA的稳定性。此外，反义RNA MYC-AS1还抑制c-MYC靶向基因LDHA的表达。总之，我们的研究项目鉴定反义RNA MYC-AS1具有肿瘤抑制因子的功能，发现了一种通过反义RNA沉默，从而激活原癌基因c-MYC的表观遗传新机制。